Control valve body of automatic transmission and manufacturing method therefor

ABSTRACT

By pouring, by means of pressure, melted liquid of magnesium or magnesium alloy into a hollow portion which is formed using a casting mold, a valve body where a channel groove for hydraulic oil for use in a speed change operation of the automatic transmission is formed. In the above, the channel grove for the hydraulic oil is formed due to a convex portion which is formed on the mold so as to project into the hollow portion. As the magnesium has small heat capacity, variation of the temperature of the mold during the cooling and heating cycle can be suppressed. Moreover, as the magnesium melted liquid has no reactivity with respect to the casting mold, the convex portion is not deteriorated. This allows employment of a mold having a thinner convex portion formed thereon, and therefore formation of a valve body having a narrower channel groove.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/596,845, now U.S. Pat. No. 7,854,250 which is a national phaseapplication of International Application No. PCT/JP2005/009114, filedMay 12, 2005, and claims the priority of Japanese Application No.2004-150931, filed May 20, 2004, the contents of all which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a control valve body of an automatictransmission, in which a channel groove for hydraulic oil for use in aspeed change operation of the automatic transmission is formed betweenpartitions, and also to a method for manufacturing the same.

BACKGROUND ART

Japanese Patent Laid-open Publication No. 2000-320502 discloses relatedart of a control valve body of an automatic transmission. According tothis related art, a valve body member which has a hydraulic oil channelgroove formed on at least one surface thereof and constituting ahydraulic circuit, and a cap member which is attached to the surface ofthe valve body member where the channel groove is formed and covers thechannel groove, are provided. On the cap member, a supporting portion isformed, which has a side surface for supporting the partition betweenthe channel grooves on the valve body member, against pressing pressureapplied from an oil channel in the form of the channel groove. With thisarrangement, the thickness of the partition formed on the valve bodymember, and accordingly the size and weight of the valve body member,can be reduced.

In addition to the above, Japanese Patent Laid-open Publication No. Hei10-238628 discloses a control valve body of an automatic transmission.Further, as other background art, Japanese Patent No. 3286224 andJapanese Patent Laid-open Publication No. Hei 11-124692 disclose amagnesium-molded product.

A control valve body of an automatic transmission is generallymanufactured through aluminum die-casting. A hydraulic oil channelgroove defined on the valve body is formed using a steel casting mold.However, in an attempt to reduce the width of the channel groove inmanufacturing the valve body through aluminum die-casting, the castingmold in use is readily deteriorated due to the reaction between thealuminum melted liquid and the steel casting mold and heat exhaustion orthe like in a cooling and heating cycle. Therefore, it is notpracticable to employ a valve body having a channel groove of a narrowerwidth.

According to Japanese Patent Laid-open Publication No. 2000-320502,where size and weight reduction of the valve body is attempted byforming a thinner partition, a problem remains that sufficient size andweight reduction of the valve body cannot be readily achieved asemployment of a channel groove having a narrower width is notpracticable due to the above-described reason.

The present invention aims to provide a control valve body of anautomatic transmission in which a hydraulic oil channel groove having anarrower width can be formed, and a method for manufacturing such acontrol valve body.

DISCLOSURE OF INVENTION

According to the present invention, there is provided a manufacturingmethod for manufacturing a control valve body of an automatictransmission where a channel groove for hydraulic oil for use in a speedchange operation of the automatic transmission is formed betweenpartitions, comprising a magnesium die-casting step of pouring, by meansof pressure, melted liquid of magnesium or magnesium alloy into a hollowportion formed using a casting mold, to thereby mold a valve body havingthe partitions formed thereon, and in the magnesium die-casting step,the channel groove is formed due to a convex portion which is formed onthe casting mold so as to project into the hollow portion.

According to the present invention, by pouring, by means of pressure,the melted liquid of magnesium or magnesium alloy into the hollowportion formed using a casting mold, a valve body where partitions forforming a hydraulic oil channel groove are formed is molded.

With the above, variation of the temperature of the mold during thecooling and heating cycle can be suppressed, and the reactivity betweenthe melted liquid and the mold can be eliminated. Therefore, accordingto the present invention, the convex portion formed on the mold forformation of a channel groove is not deteriorated. This allowsemployment of a thinner convex portion, and accordingly, formation of ahydraulic oil channel groove having a narrower width.

In the method for manufacturing a control valve body of an automatictransmission according to the present invention, a piercing pin whichprojects into the hollow portion and pierces through the convex portionis provided on the casting mold, and in the magnesium die-casting step,a valve hole for allowing the valve to pierce through the partitions isformed by the piercing pin.

With this arrangement, it is possible to reduce the force (side force)which is perpendicular to the shaft of the valve and acts on the valvepiercing through the partitions.

According to another aspect of the present invention, there is provideda control valve body of an automatic transmission where a channel groovefor hydraulic oil which is used in a speed change operation of theautomatic transmission is formed between partitions, wherein a valvebody having the partitions formed thereon is made using magnesium ormagnesium alloy.

According to the present invention, the valve body where partitions forforming a channel groove for hydraulic oil are formed is made usingmagnesium or magnesium alloy. This enables formation of a channel groovefor hydraulic oil having a narrower width.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view schematically showing a structure of acontrol valve body of an automatic transmission according to anembodiment of the present invention;

FIG. 2 is a cross sectional view schematically showing a structure of acontrol valve body of an automatic transmission according to theembodiment of the present invention;

FIG. 3 is a cross sectional view schematically showing a structure of amagnesium die-casting device used in carrying out a method formanufacturing the control valve body of the automatic transmissionaccording to the embodiment of the present invention;

FIG. 4 is a cross sectional view schematically showing a structure of amagnesium die-casting device used in carrying out a method formanufacturing the control valve body of the automatic transmissionaccording to the embodiment of the present invention; and

FIG. 5 is a cross sectional view explaining a side force applied to thevalve.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, a preferred embodiment of the present invention willbe described with reference to the accompanied drawings.

FIGS. 1 and 2 are cross sectional views schematically showing astructure at different positions of a control valve body of an automatictransmission according to an embodiment of the present invention. Avalve body 10 according to this embodiment has a plurality of partitions12 formed on a base surface 10-1 of the valve body 10 thereof so as toproject in a substantially vertical direction thereto, so that a channelgroove 14 for hydraulic oil, which is used in a speed change operationof the automatic transmission, is defined between the partitions 12. Itshould be noted that FIGS. 1 and 2 show only a part of the valve body10, and that the overall shape of the valve body 10, which can berealized in a known shape, is not shown. The valve body 10 according tothis embodiment is used in a hydraulic control circuit for an automatictransmission such as a multi-speed AT, a CVT, or the like.

As shown in FIG. 2, a valve hole 18 is formed on some of the partitions12, so that the valve 16 passes through the valve holes 18 to therebypass through the partitions 12 in the substantially vertical direction.When the valve 16 slides in the substantially vertical directionrelative to the partitions 12 (that is, the direction substantiallyparallel to the base surface 10-1 of the valve body 10), oil grooves foruse in a speed change operation of the automatic transmission can beswitched.

In this embodiment, the valve body 10 having the partitions 12 formedthereon is made using magnesium or magnesium alloy. As an example ofmagnesium alloy, AZ group (AZ91D and so forth), or AM group (AM60 B anso forth) may be employed here. In addition, AS group (AS21 and soforth) having heat resistance imparted, or heat resistant alloy with Ca,Sr, RE (Ce, La, Pr, Nd), Sn or the like added thereto may also beapplicable. Any alloy containing magnesium as a main component can beused as the material of the valve body 10 according to this embodiment.

In the following, a method for manufacturing the valve body 10 accordingto this embodiment will be described. The valve body 10 according tothis embodiment can be manufactured through steps including a magnesiumdie-casting step.

FIGS. 3 and 4 are cross sectional views schematically showing astructure at different positions of a magnesium die-casting device whichis used in carrying out a method for manufacturing the valve body 10according to this embodiment. The die-casting device in this embodimenthas a steel mold including a fixed side die 21 and a moving side die 22.The fixed side die 21 and the moving side die 22 together form a hollowportion 23 for molding the valve body 10.

A plurality of convex portions 27 are formed on the moving side die 22,which project into the hollow portion 23. Further, as shown in FIG. 4, amoving pin 28 is provided to the moving side die 22, which projects intothe hollow portion 23 while piercing through some of the convex portions27 in the substantially vertical direction.

In the magnesium die-casting step, the melted liquid 29 of magnesium ormagnesium alloy is poured into the hollow portion 23 by means ofpressure from the plunger 26 for molding the valve body 10. In themolding, the channel groove 14 is formed due to the convex portion 27,and the melted liquid 29 poured into the space between the convexportions 27 forms the partition 12. The valve hole 18 is formed due tothe moving pin 28. It should be noted that as the melted liquid 29 ofmagnesium alloy, the melted liquid 29 of the above described materialsmay be employed.

After the melted liquid 29 having been poured into the hollow portion 23by means of pressure is consolidated through cooling, the moving pin 28is pulled out from the moving side die 22, and the moving side die 22 ismoved to thereby release the hollow portion 23. Then, known machining iscarried out on the valve body 10 which is molded through magnesiumdie-casting. Through the above-described steps, the valve body 10according to this embodiment can be manufactured.

Here, a case in which the valve body 10 is molded through aluminumdie-casting is considered. In this case, due to the large heat capacityof the aluminum, the temperature of the dies 21, 22 may vary largely ina cooling and heating cycle. Further, the reaction between the meltedaluminum liquid and the steel dies 21, 22 readily leads to formation ofreactant on the surface of the dies 21, 22. As a result, the dies 21, 22(in particular, the convex portion 27 thereof) are readily deteriorated.Therefore, in the case where the valve body 10 is molded throughaluminum die-casting, a die 22 having thinner convex portions 27 formedthereon is not appropriately employed. This makes it difficult to form avalve body 10 having a channel groove 14 with a narrower width.

Meanwhile, in this embodiment, magnesium die-casting is employed inmolding of the valve body 10 having partitions 12 formed thereon. Asmagnesium has a smaller heat capacity than aluminum, the variation ofthe temperature of the dies 21, 22 in the cooling and heating cycle canbe suppressed. Moreover, as the melted magnesium liquid 29 has noreactivity with respect to the steel dies 21, 22, deterioration of thedies 21, 22, in particular, of the convex portion 27 thereof, can besuppressed. Therefore, according to this embodiment, as the convexportion 27 is not deteriorated, a thinner convex portion 27 can beemployed. This enables formation of a valve body 10 having a channelgroove 14 having a narrower width d, and therefore, size reduction ofthe valve body 10 can be achieved. It should be noted that, in thisembodiment, typically, the width d of the channel groove 14 can bereduced to smaller than 3 mm.

Further, in this embodiment, the use of magnesium, which has smallerrelative density than aluminum, as the material of the valve body 10enables reduction of the weight of the valve body 10.

In addition, in the case where the valve body 10 is molded throughaluminum die-casting, it is difficult to ensure a smaller draft angledue to the reactivity between the aluminum melted liquid and the steeldies 21, 22. Specifically, when there is a draft angle defined on thepartition 12, as shown in FIG. 5, the width of the channel groove 14becomes wider as it goes away from the base surface 10-1 of the valvebody 10. In this case, in consideration of the force (a side force)which is perpendicular to the shaft of the valve 16 and acts on thevalve 16 due to the pressure of the hydraulic oil having been pouredinto the channel groove 14, the side force A due to the pressure by thehydraulic oil near the tip end side of the partition 12 (upper in FIG.5) is larger than the side force A′ due to the pressure of the hydraulicoil near the base surface side 10-1 (lower in FIG. 5). In other words, aside force which is directed from the tip end side of the partition 12toward the base surface 10-1 side thereof acts on the valve 16. Thisside force causes the friction of the valve 16 to increase, leading todeterioration of the oil groove switching capability.

Meanwhile, in this embodiment, as the valve body 10 having partitions 12formed thereon is molded through magnesium die-casting, the reactivitybetween the magnesium melted liquid 29 and the steel dies 21, 22 can beeliminated. This makes it possible to ensure a smaller draft angle ofthe partition 12. As a result, the channel groove 14 having constantwidths on the tip end side of the partition 12 and the base surface 10-1side can be formed. This makes it possible to reduce the above-describedside force which acts on the valve 16. Therefore, in this embodiment,the friction of the valve 16 can be reduced, and the oil grooveswitching capability can be enhanced. It should be noted that in thisembodiment, typically, the draft angle of the partition 12 can bereduced to smaller than two degrees.

Further, in this embodiment, beside realization of a smaller draftangle, molding of the valve 10 through magnesium die-casting enablesreduction of consumption of the mold release agent.

It should be noted that, although an embodiment to render the presentinvention into practice has been described in the above, the presentinvention is not limited to such an embodiment, and that a variety ofmodifications can be made to the present invention within the scope andgist of the present invention.

The invention claimed is:
 1. A control valve body of an automatictransmission where a channel groove for hydraulic oil for use in a speedchange operation of the automatic transmission is formed betweenpartitions, wherein the control valve body is manufactured by amanufacturing method comprising: a magnesium die-casting step ofpouring, by means of pressure, melted liquid of magnesium or magnesiumalloy into a hollow portion formed using a casting mold, to thereby molda valve body having the partitions formed thereon, and wherein in themagnesium die-casting step, the channel groove having a width of lessthan 3 mm is formed due to a convex portion which is formed on thecasting mold so as to project into the hollow portion, and a draft angleof the partitions is smaller than two degrees.